In terms of what to put aside, the above advice looks good to me. The link below will take you to HMRC's own website on what to do when you are self-employed - I suggest you work your way through the (relevant) Q&As.
http://www.hmrc.gov.uk/sa/selfemp.htm#new1
One of the first things you will find you have to do is to tell HMRC that you are now self-employed.
The only practical change is that HMRC will send you a self-assessment form each year to fill in. Complete this in good time and they will do the actual tax calculation for you.
In practical terms, there isn't a lot of difference in what you actually pay. You will end up paying the equivalent of employee's NI contribution as well as income tax at the same rate as before. However you will be able to offset expenses against the income you receive. One of these expenses is the cost of you getting to your work and back - because your normal place of work is now your home. Depending whether you have a long commute journey, this might avoid you paying quite a bit of tax. HTH